from times to times i hear people saying this word on TV shows and so on.
is it really an informal word and can be used fearlessly?
do people speak like this daily and colloquially?
it means "absurd" or "ridiculous", right?
I think it is flavour of the month as words go. Just like children and adolescents would not use the word 'excellent' ordinarily, suddenly it caught on and 'hip' went out and one of the words that came in was 'excellent'.
Just like things 'suck', now they're 'ludicrous'. The point is, they don't care what it actually means - it means 'no good' versus something is 'cool' or whatever the word is today for something being 'good' = meeeting approval of the young crowd - 'in', 'hot' or whatever.
I'm not a teacher, but I'd say "yes" to all your questions. It can be used informally, with confidence that it will be understood. It does mean "absurd" or "ridiculous". It's likely that it's not used quite as often as those two, but it's still not a rare word at all.